More than three million people are estimated to have attended a Mass led by Pope Francis on Copacabana beach in Rio de Janeiro at the end of the Catholic youth festival.
Latin America's first pontiff was given a rock star welcome amid chants of "Long live the Pope" in a carnival atmosphere.
The event marked the end of a five-day visit to Brazil by the Pope. It was his first foreign trip since becoming pontiff in March.
A BBC correspondent said almost every inch of the 2.5 mile beach was occupied before the Mass.
Many of the pilgrims slept on the beach after an all-night vigil there.
Pope Francis encouraged young Catholics to get out of their parochial boundaries in order to help others.
"Go and don't be afraid of serving," he said. "Jesus did not gather the Apostles so they lived in isolation. He called them so they formed a group, a community."
Pope Francis announced the next Catholic youth festival would be held in the Polish city of Krakow in 2016.
